After several months and several hundred dollars, the hot tub is now repaired, filled, and full of clean, hot water. The acrylic shell developed a small fatigue crack along the left edge of the captain's seat where the steps entered the tub. This occurred last June, and I repaired the tub myself with marine sealant as I wasn't so much worried about the cosmetics of the repair, and I figured that if it was good enough for the hull of a boat below the waterline, it would probably be fine for the static forces on a hot tub.
Unfortunately, I didn't take into account the possibility that someone might slip and fall into the captain's seat and cause a catastrophic failure of the repair. Which is exactly what happened. And since this happened in late November, I just drained the tub, covered, and let it sit through the winter rains.
With the recent good weather, though, it was time to get the tub back in service, so I got the Miracle Surface repair folks to come out and repair the acrylic surface in the tub.
They did a very nice job and managed to get the color and texture very close to the original. It's not perfect, but it's a much better match than the marine patch that I used. It also appears to be much stronger. The patch required 7-14 days of cure time, so I took that time to research how to best reinforce the patch from the underside. The surface patch made the tub water tight, but I needed to add structural strength underneath to keep the tub from cracking again.
From my research, I determined two things: 1) Hot tub shells don't normally crack to the point where they leak and 2) Most people don't want to fix them. I learned an additional bit of information as well - I had to use a fiberglass repair kit such as those used on cars and boat hulls. This meant using a resin and hardener and fiberglass matting or cloth in order to get the structural strength required. The fun part was that I would be working inside the hot tub shell and applying the patch to a horizontal overhead surface.
The interior repair actually wasn't so bad. I should have used fiberglass cloth instead of fiberglass mat, and I should have mixed my resin and hardener is smaller batches (the first large batch hardened before I could apply all of it), but all in all the repair went quickly and time will tell if the structural reinforcement will prevent a recurrence of the crack.
Once the structural repairs were complete it was a simple matter to fill the tanks, turn on the system, ensure the recirculation pump hadn't been damaged by the loss of water during the previous failure, and leak check the repairs. Once the water had been in the tub for 24 hours with no leakage, I added the chemicals and made the tub available for use.
As you can see from the photos, I like to use the tub for various photo projects. It makes a natural setting for swimsuit and figure shots, and provides privacy for the shoot. With any luck, I 'll get to use the tub for both sore muscles and photography during the rest of the spring, summer and early fall.